This invention relates to apparatus for measuring operating parameters of a high voltage power conductor. More particularly, it relates to a radio transmitting sensor which are mounted on the transmission lines. The sensors normally derive their power through electromagnetic induction using the magnetic field generated as a result of current flowing through the transmission line conductor. Transmission line sensors of the above type are disclosed in the U.S. Pat. No. 4,384,289, of Howard R. Stillwell and Roosevelt A. Fernandes entitled Transponder Unit for Measuring Temperature and Current on Live Transmission Lines, issued May 17, 1983, which patent is incorporated herein by reference.
Various power line sensors have been disclosed in the prior art. For example, see U.S. Pat. Nos. 3,428,896, 3,633,191, 4,158,810 and 4,268,818. Sensors of this type and of the improved form disclosed in the above-identified Stillwell and Fernandes patent have been proposed for dynamic line rating of electrical power transmission lines.
The power line sensor available in the prior art measure quantities associated with operation of the overhead line such as voltage on the conductor, current flow in the conductor, conductor temperature and ambient temperature. The information gathered is transmitted to a local ground station. Data from various ground receivers is transmitted to a central control station where the information is analyzed. Based on this analysis, the entire power system is controlled with power being supplied to the various transmission lines in accordance with their measured parameters.
The compact toroidal-shaped sensor modules, disclosed in U.S. Pat. No. 4,384,289 and in the prior copending applications referenced above, contain the sensor electronics, power supply and transmitter circuits, and hardware for attaching the sensors to the transmission lines. Under normal operating conditions, power for the sensor module is derived from the transmission line conductor and converted into regulated supply voltages for the sensor electronics and transmitter. However, the harsh environment of power transmission lines subjects the sensor module to power supply fluctuations due to a variety of transient line conditions. The module electronics include a number of metal-oxide-semiconductor (MOS) integrated circuits. These circuits are sensitive to variations in supply voltage and may enter a power-fail state or may be locked into an inoperable state if the sensor module experiences a power fluctuation or some other abnormal operating event.
In accordance with the present invention, the transmission line sensor module is provided with an operation monitoring circuit, often called a watchdog circuit. The watchdog circuit prevents the sensor module from being locked in an inoperable state after the occurrence of a transient event that adversely effects the MOS integrated circuits. The circuitry of the present invention senses a condition that indicates the integrated circuits are operating in an abnormal mode. In response to this sensed condition, the supply voltage to the circuits is shut off for a predetermined time period and then turned back on. This feature effectively resets the integrated circuits to a known operational state thereby permitting a normal operational sequence to begin.
It is also possible that a non-critical integrated circuit will enter a power-fail state without affecting the operating sequence of the module in a manner that is easily detectable. In this situation, the MOS integrated circuit in a power-fail state will draw excess power. The present invention includes current limiting circuitry which reduces the supply voltage to the integrated circuits when a failed circuit attempts to draw excess power. Thus the current limiting circuitry functions as a secondary watchdog circuit since the reduced voltage will effectively reset all the integrated circuits, including the circuit in a power-fail state.
It is therefore an object of the invention to provide a transmission line sensor module which can continue to operate after the occurrence of a transient line condition or interrruption in the normal operating sequence.
Another object is to provide a watchdog circuit which monitors the module's operation to detect a variation in the normal operating sequence.
A further object of the invention is to provide monitoring circuitry that is responsive to detection of an abnormal operating sequence of resetting the module's integrated circuits.
Another object of the invention is to provide circuitry which resets the module's electronics to a known operational state by shutting off power to the electronics and subsequently turing power back on.
Still another object of the invention is to reset the module's electronics in the event that an individual integrated circuit enters power-fail mode without altering the normal operating sequence of the sensor modules.